FDA: False Positives Common with LabCorp Zika Test

Posted: December 28, 2016

LabCorp Zika Testing Provides Increased False Positive Results. More false positives have been associated with preliminary testing for the Zika virus through LapCorp for pregnant patients. The U.S. food and Drug Administration (FDA) warns that clinicians should not consider these tests as a valid confirmation that a patient has been infected with the virus.

The Zika test in question, known at “ZIKV Detect” is considered a presumptive test, which means that it must be confirmed by the U.S. Centers for Disease Control and Prevention (CDC) or a qualified laboratory, wrote MedScape. Clinicians are advised not to rely on ZIKV Detect results as the only basis of “significant patient management decisions,” the FDA indicated in a MedWatch safety communication. Pregnant women should not make healthcare decisions based on the partial information and caution is recommended as the Zika virus may lead to disastrous birth defects, including microcephaly and loss of pregnancy.

According to the Mayo Clinic, microcephaly is a rare, neurological condition in which the baby’s head is considerably smaller that the heads of other babies of the same age and sex and is typically caused because the brain develops abnormally in the womb or does not grow as it should following birth. Children diagnosed with microcephaly are also typically diagnosed with developmental issues, including delays in speech and movement, coordination and balance, Dwarfism or short stature, facial distortions, hyperactivity, mental retardation, or seizures. There is no treatment, but early intervention may help with obtaining supportive therapies.

The World Health Organization (WHO) notes that scientific consensus indicates that Zika virus is a cause of microcephaly and Guillain-Barre syndrome. Ties to other neurological complications are under review.

Confirmatory testing may take a month to perform; however, if the CDC is aware that the sample is from a pregnant woman, the results may be made more rapidly. Clinicians should always advise the laboratory that is conducting the presumptive ZIKV Detect test if the patient is a pregnant woman so that confirmatory testing by the CDC or a qualified laboratory may be prioritized, MedScape noted.

ZIKV Detect is manufactured by InBios International and is meant to detect the Zika virus IgM antibodies in human sera (serum) collected from patients who either have a history of Zika infection, signs and symptoms of the infection, or a history of travel or residence in an active Zika transmission zone. The FDA approved ZIKV Detect in August and the test is the first commercially available serologic IgM test for Zika, according to MedScape. LabCorp and other commercial laboratories have switched to ZIKV Detect from a CDC assay (a type of investigative laboratory procedure) authorized at the beginning of 2016.

A confirmatory test is needed for both CDC’s assay and the ZIKV Detect. Previously, most presumptive positive results from each have proven accurate; however, this has not been the case with the ZIKV Detect testing conducted by LabCorp, according to the FDA. In fact, the CDC reported that the confirmation rate of the presumptive positive results captured by LabCorp through ZIKV Detect is less than 50 percent.

The FDA indicated that it has not determined if the high rate of false positives is related to the ZIKV Detect test or to LabCorp. Tests for Zika IgM antibodies continue to remain useful for ruling out Zika exposure, but they always require confirmation, the FDA noted, according to Medscape.

What is the Zika Virus?

In its May 2016 interim advice, the CDC explained that the Zika virus, a single-stranded RNA virus, is transmitted by a mosquito-borne flavivirus that is closely related to dengue, West Nile, Japanese encephalitis, and yellow fever viruses and share similar symptoms of infection, transmission cycles, and geographic distribution. Diagnostic testing involves both molecular and serologic methods; however the results of Zika virus antibody testing may be challenging to interpret due to potential cross-reactivity with related flaviviruses. This may impede identification of the specific virus, especially when the person being tested was previously infected with, or vaccinated against, a related flavivirus.

Pregnant women who have been advised of laboratory evidence of a Zika virus infection should undergo further evaluation, be managed for potential adverse pregnancy outcomes, and be reported to the U.S. Zika Pregnancy Registry or the Puerto Rico Zika Active Pregnancy Surveillance System for clinical follow-up, the CDC indicates. It is recommended that health care providers consult with state or local public health authorities for help with test result interpretation.

All patients with clinically suspected dengue must undergo proper health management to minimize risk for hemorrhage and shock. Also, if serologic testing shows a recent flavivirus infection that may be the result of either Zika or dengue virus, then patients should be clinically managed for both infections as they may have been infected with either virus.

According to WHO, the Zika virus disease is caused by a virus that is typically transmitted by Aedes mosquitoes. Symptoms include mild fever, skin rash, conjunctivitis, muscle and joint pain, malaise, or headache and typically last from two to seven days. The Zika virus disease incubation period-time from exposure to symptoms-remains unclear; however, it is believed to be a matter of a few days.

Aedes mosquitoes typically bite during the day, peaking in the early morning and late afternoon-evening. This is the same mosquito that transmits dengue, chikungunya, and yellow fever. Transmission of Zika virus is possible via sexual activity and blood transfusion, which are being investigated. That the Zika virus is transmittable by sexual intercourse is of concern given the tie between Zika virus infection and adverse pregnancy and fetal outcomes, notes WHO. Protection against mosquito bites is critical to prevent Zika virus infection, including to one’s person and home areas.

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